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Re: Plot using DSolve HELP

  • To: mathgroup at smc.vnet.net
  • Subject: [mg104408] Re: [mg104388] Plot using DSolve HELP
  • From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
  • Date: Sat, 31 Oct 2009 01:48:49 -0500 (EST)
  • References: <200910300717.CAA27667@smc.vnet.net>

Hi

On Fri, 2009-10-30 at 02:17 -0500, Becky wrote:
> I have a problem with what I am showing below.
> 
> Step one is my equation.
> eq = i * v[t]/r +c v'[t]


you called it "equation", you name the variable "equation" but it's not
an equation.
Basic example:

eq = v'[t] == 3.4*v[t]
sol = v[t] /. DSolve[{eq, v[0] == 1}, v[t], t];
Plot[sol, {t, 0, 2}]

Cheers
Patrick


> Step two I want to solve it, using DSolve, and put my values in as shown.
> Please note, that "i= 0", and my IC is v[0]== -70.
> 
> sol=v[t]/.DSolve[{eq/.{c->3, i->0, r->2.5} ,v[0]==-70}, v[t], t]
>  {-70 *-0.133333 t}
> The results are shown above.
> 
> Thus next step is to plot it.
> p1=Plot[sol,{t,-20,140}]
> 
> My problem is that I get a line from -70 on the vertical axis going in a
> curve up to the horizontal axis out to 140.  The vertical axis is "v" and
> the horizontal is "t".
> 
> What am I doing wrong?
> 
> Thanks
> Jake
> 
> 



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